the greyed out section is meant to be linked to the WHOLE of section 6.1.2, not just the subsections. However, it's true that it was important to link it to chapter 22.214.171.124.
To be clear: you MUST have two workers for this action; In your last sentence, you state that:
"Another possibility which is not explicitly covered, but in principle is fairly obvious, is the case that you have only one worker left and do not have one at the Architect. You place your first worker at the Architect but then you wouldn't have a second worker to place at the new building so you couldn't build the building at all and would instead have to move one of your influence markers up a step (or choose a different action entirely).
so no, you cannot do that. The rules state that
" you may not build a Building during this action"
so you have to be able to do the full action. Since in your example, you don't have the second worker to place it on the building you just built, you're not doing the action fully, so this isn't allowed; You have to choose another action. The "Build the Building" in this section refers to the Architect.